The present invention relates generally to fuel injection systems for internal combustion engines, and more particularly to, a method and apparatus for installing fuel injector coefficient data, that is specific to a particular fuel injector, in an engine controller when replacing a fuel injector.
In typical prior art fuel injected engines, it is generally considered desirable that each injector deliver approximately the same quantity of fuel in approximately the same timed relationship to the engine for proper operation. It is well known that problems arise when the performance, or more particularly the timing, and the quantity of fuel delivered by the injectors diverge beyond acceptable limits. For example, injector performance deviation or variability will cause different torques to be generated between cylinders due to unequal fuel amounts being injected, or from the relative timing of such fuel injection. Further, knowledge that such variations occur, requires engine system designers to account for this variability by designing an engine system to provide an output equal to the maximum theoretical output less an amount due to the worse case fuel injector variability rather than design a system for peak or maximum cylinder pressures or output.
Various attempts have been made for solving these problems associated with fuel injectors. One straight forward approach is to simply adhere to rigid manufacturing and test procedures to assure each injector meets a rigid desired design specification. Unfortunately, the increased manufacturing and assembly costs and the low yield of acceptable units makes this approach undesirable.
Sophisticated electronic equipment and control have made it possible to better control the problem of timing and delivery variations of similar fuel injectors. One such control involves compensating for individual injector variations and includes an electronic control module having a memory for storing compensation signals for each injector. The compensation signals used are derived from observed performance parameter values taken at a number of operating conditions and further include a plurality of sensors for detecting at least one and preferably a number of operating parameters. One or more operating parameter signals are then generated which are then provided to the memory. The electronic control module adjusts the base fuel delivery signal for each injector as a function of the compensation data signal for that injector. Unfortunately, some of the more complex and advanced fuel injectors now being manufactured do not follow readily predictable fuel-flow characteristics with increased pulse-width inputs, as was the case with earlier style injectors. Consequently, unless individual compensation signals are determined for an extremely large number of operating points resulting from different pulse widths, such systems would not operate satisfactorily with those advanced fuel injectors. Also, the amount of memory to store a sufficiently large number of compensation signals covering the full range of fuel injector operation would be excessively large, and the cost involved in the necessary testing to determine such a large number of compensation signals would be unacceptable.
The advanced fuel injector are very complicated and difficult to manufacture and therefore it is very difficult to have consistent operating characteristics between injectors even though they are intended to be substantially identical. Further, although varying pulse width of a control signal is used to vary the amount of fuel an injector provides to a cylinder (hereinafter referred to as fuel flow or flow rate), a performance curve of these complicated fuel injectors (fuel flow vs. pulse width) cannot be accurately defined by a second-order polynomial as can some older types of fuel injectors. Instead, the advanced fuel injectors must be defined by a third-order polynomial. Consequently, determining the pulse width for a desired RPM by extrapolating between sample data points does not provide satisfactory performance. By calculating the pulse width for each fuel injector individually for each desired RPM setting, substantially increased effectiveness of these advanced complicated fuel injectors can be achieved.
To determine the proper pulse width for a desired RPM for each fuel injector used in the engine, the coefficients for a third-order polynomial, which most closely define a performance curve of each fuel injector, are stored in a read/write memory associated with a specific cylinder in the engine. In addition, the basic form of a third-order polynomial is also stored and available for use by a microprocessor in the ECU (electronic control unit). The microprocessor retrieves the coefficients for each fuel injector and then uses the coefficients for the specific fuel injector to solve the basic third-order polynomial to determine the appropriate pulse width for a given throttle position or desired RPM thereby causing the correct amount of fuel to be injected into the cylinder to achieve the desired RPM.
Before the coefficients of a third-order polynomial representing the performance curve of a specific fuel injector can be stored in the read/write memory so as to be retrievable by the engine ECU, they must be determined. It is also important that a failed fuel injector can be replaced by a new injector which will also operate effectively with any cylinder.
Accordingly, each fuel injector is tested on a test flow bench by applying a signal pulse having a selected minimum width and then measuring the fuel flow rate. The pulse width is then increased a known amount and the resulting fuel flow rate again is measured. The process is repeated a number of times, such as 8 to 10 times, to obtain a series of data points which relate pulse width to a fuel flow rate.
These data points are then used to determine a third-order polynomial such as ax3+bx2+cx+d=0, which can also be used to define a performance curve representative of the fuel flow output of the fuel injector for any pulse width. The pulse width can then be correlated to the desired RPM. The degree of fit (R2) of said data points to the performance curve defined by the third-order polynomial is also determined within selected limits such that those fuel injectors which fall outside of the selected degree of fit are discarded. The coefficients of at least a portion of those fuel injectors which fall within the selected degree of fit are used to determine a nominal performance curve. Selected upper and lower limits are then set with respect to the nominal curve at each of the pulse-width values used to test the multiplicity of fuel injectors and then the fuel injectors are compared with the nominal curve to determine if the performance curve of each individual fuel injector stays within or exceeds the upper and lower limits of the nominal curve. Those that stay within the upper and lower limits are then used for assembly and replacement parts.
It will be appreciated by those skilled in the art that the third-order polynomial coefficients for each curve representing a fuel injector may be determined by various techniques including manual calculations. A regressive analyzer can also be particularly useful. Such a regressive analyzer can provide the degree of fit according to a least squares method wherein R2=1 is considered a perfect fit. A degree of fit for R2 greater than 0.998 has been found to provide a suitable threshold for attaining or discarding fuel injectors as discussed above.
When an engine is initially manufactured, the coefficient data can be determined empirically by any such method. Coefficient data for each of the particular fuel injectors to be installed in the engine is written into read/write memory for use by the ECU microprocessor. To subsequently replace a failed fuel injector, it is then necessary to replace the third-order polynomial coefficient data to the read/write memory over the coefficient data of the failed fuel injector, so that during future operations of the engine, the new coefficient data will be available for use by the ECU microprocessor. To simplify this service process, the prior art preprograms a set of service injector coefficient data in the ECU memory and manufactures all service injectors under stringent tolerance requirements so as to function with the known service coefficients. In this manner, whenever a fuel injector fails, one of the special service fuel injectors is installed, and the ECU is simply instructed to use the service coefficient data for that particular cylinder. While this approach results in satisfactory operating conditions, it is relatively costly. That is, to manufacture each service injector with such stringent tolerances so that the flow rate satisfies a desired performance curve dictated by the fixed service injector coefficient data, results in a relatively expensive replacement fuel injector.
It would therefore be desirable to use an off-the-shelf, production fuel injector with wider tolerances so that custom coefficient data for that particular injector can be written to the memory location for the targeted cylinder, and use of the coefficient data can be restricted to give a relative level of confidence against misuse.
The present invention relates to a method and system to replace fuel injector coefficient data in an ECU of a fuel injected engine to enable use of the more economical production fuel injectors that overcomes the aforementioned problems.
The present invention provides a way to readily replace the aforementioned advanced fuel injectors in an engine, using a standard production fuel injector, that maintains effective and efficient fuel injector operation. The present invention includes storing coefficient data that is specific to a particular fuel injector, and providing that coefficient data, together with the associated fuel injector, to a customer for replacement in an engine. A computer program is also supplied to read out the existing coefficient data from the ECU before writing the replacement coefficient data so that restoration of the existing coefficient data, and the associated fuel injector, can be accomplished if the replacement fuel injector does not correct the service problem experienced. The system includes a log file to prevent misuse of the coefficient data by tracking how the program and data are used. That is, once the replacement coefficient data is used, the only way to reuse the data is if the original existing coefficient data is restored in the ECU from which it originated. If the data is restored, and it is assumed that the original fuel injector is reinstalled in the original cylinder from which it came, the program allows the reuse of the replacement coefficient data.
Therefore, in accordance with one aspect of the invention, a system to replace fuel injector data in an ECU when replacing a fuel injector in an engine is disclosed. The system includes a computer readable storage medium operable with a service computer connectable to transmit data to an ECU of a fuel injected engine. The computer readable storage medium has thereon replacement fuel injector coefficient data that corresponds precisely to the fuel injector to be installed in the engine. The computer readable storage medium also has a computer program which, when executed by the service computer, causes the service computer to write the replacement fuel injector coefficient data to the ECU for a specified replacement fuel injector.
In accordance with another aspect of the invention, a fuel injector service pack is disclosed that includes a single replacement fuel injector and a computer readable storage medium. The single replacement fuel injector of the service pack has a fuel flow characterized by a custom set of coefficients that are experimentally determined for that particular fuel injector. The computer readable storage medium has stored thereon a data file containing a serial number and the custom set of coefficients for that single replacement fuel injector. The storage medium also has a computer program that includes instructions which, when executed by the computer, causes the computer to allow identification of a cylinder in the fuel injected engine for which a fuel injector is to be replaced. The computer is also caused to read and store existing fuel injector coefficient data from an ECU of the fuel injected engine and write the custom set of coefficients from the data file to the ECU for use with the single replacement fuel injector.
The computer readable storage medium also includes a log file that is used by the computer program to track how the data file is used and ensure that the custom set of coefficients are not used with another fuel injector. That is, the computer program of the service pack causes the computer to allow restoration of the existing fuel injector coefficient data if the single replacement fuel injector did not solve a user problem and restricts use of the existing fuel injector coefficient data, and thus restricts use of the original fuel injector, to ensure that the original fuel injector is only used with its existing fuel injector coefficient data. The replacement fuel injector is then also only used with the replacement fuel injector coefficient data. The restoration process is allowed by writing a serial number of the single replacement fuel injector to the ECU when the custom set of coefficients are written to the ECU. The use of the data is restricted by reading and comparing each fuel injector serial number in the ECU with the serial number of the single replacement fuel injector as stored in the data file if the last use of the computer program was to replace data. If a match is present, the service pack software allows the existing fuel injector coefficient data to be written back into the ECU and directs that the original fuel injector be installed in the cylinder identified so that the ECU uses the existing fuel injector coefficient data with the original fuel injector.
In accordance with yet another aspect of the invention, a method of servicing an engine requiring fuel injector replacement includes identifying a fuel injector in need of replacement by cylinder number, establishing communication between a service computer and an ECU of the engine, and downloading ECU, engine, and fuel injector data from the ECU to the service computer. The method next includes writing replacement fuel injector coefficient data to the ECU for a replacement fuel injector for the specific cylinder identified. The method next includes installing the replacement fuel injector in that cylinder of the fuel injected engine.
In accordance with yet another aspect of the invention, a method is disclosed for providing replacement fuel injectors for a fuel injected engine that includes the steps of supplying a production fuel injector with relaxed tolerances as compared to a standard service fuel injector, and acquiring a set of coefficients that characterize a performance curve for that particular production fuel injector. The method of providing replacement fuel injectors also includes writing the set of coefficients to a transportable computer readable medium and providing a computer program on a transportable computer readable storage medium that, when executed, causes the computer to load the set of coefficients into an ECU of an engine in which the production fuel injector is to be installed.
Preferably, the method includes the additional steps of reading and storing existing fuel injector coefficient data from the ECU and allowing restoration of the existing fuel injector coefficient data while at the same time restricting use of the existing fuel injector coefficient data and the original fuel injector by writing a serial number of the replacement/production fuel injector to the ECU. Upon a request to restore data, the method includes reading data and comparing each fuel injector serial number in the ECU with the serial number of the replacement/production fuel injector. If a match is present, the method includes allowing the existing fuel injector coefficient data to be written back to the ECU, and then directing that the original fuel injector be installed in the cylinder identified.
The method and apparatus of the present invention allows for the use of a more economical production fuel injector when servicing an engine in the field. These production fuel injectors can be manufactured with relaxed tolerances since a specific set of coefficients are determined experimentally and supplied for each injector such that the coefficients of a third-order polynomial result in a desired performance curve of fuel flow versus pulse width, as previously described.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.